Singlet Spin State Drives [V]-Carbene To Catalyze Olefin Metathesis: A Computational Analysis

Abstract

Olefin metathesis is a crucial reaction typically catalyzed by Mo and Ru metal-carbene complexes. Catalysts based on 3d metals have recently attracted much interest due to their abundance, low toxicity, and inexpensive cost. Recently prepared vanadium-carbene complexes with analogous ligands to those of the Schrock carbenes were shown to be effective catalysts for norbornene's ring-opening metathesis polymerization (ROMP). In this work, we employ density functional theory (B3LYP) calculations to explore the reaction mechanism and the energetic performance of the V V (CHSiMe 3 )(NC 6 H 5 )[OC(CF 3 ) 3 ]-(PMe 3 ) 2 (D) complex in catalyzing the ROMP of norbornene. Calculations revealed that the reaction takes place in the singlet spin surface through the classical olefin metathesis mechanism. The electronic analysis indicates the absence of valence electrons in the metallic vanadium d 0 center as a cause in favoring the singlet spin state. The deactivation pathways toward cyclopropanation and βhydride elimination were calculated, and they showed higher barriers than those for olefin metathesis. The replacement of the carbene substituent −SiMe 3 by the substituent −CMe 3 was also analyzed, showing no considerable differences regarding previous catalysts. Our results suggest that the cross-metathesis reaction of styrene catalyzed by the D complex is viable since it presented a potential energy surface similar to that observed in the ROMP reaction of norbornene. The potential energy surfaces of the ROMP reaction catalyzed by D and a Schrock catalyst indicate that the classic molybdenum catalyst favors lower energy barriers compared to vanadium catalysts.

Unraveling the Compounded Interplay of Weakly and Strongly Coordinating Ligands in G3-Catalyzed Living Metathesis Polymerization: toward Well-Defined Polynorbornene at Ambient Temperature

“…Meanwhile, the relatively low energy barrier of ligand dissociation/recombination indicates a reversible step . The energy of the transition state for the formation of metallacyclobutane ( TS ) was calculated to be the highest energy (16.27 kcal/mol) in the free energy profile, which also was in accordance with previous studies. ,, The correlation of temperature and relative free energies of the possible intermediates was calculated as well (Figure S21), suggesting that the ROMP mechanism is independent of temperature.…”

Role of Electronic and Steric Effects on Ruthenium Catalysts with Bulky NHC Ligands and Relationship with the Z-Selectivity in Olefin Metathesis

“…Cross-metathesis (CM), Ring Closing Metathesis (RCM), and Ring Opening Metathesis Polymerization (ROMP) are outstanding in industrial processes [6,7]. These reactions are mediated by Ru, Mo-, V-, and W-based carbene-type catalysts [8][9][10][11]. CM is an equilibrium process between two terminal alkenes, giving rise to a mixture of olefins with trans-(E) or cis-(Z) isomerism (Figure 1a).…”